Understanding the 8085 Microprocessor Pin Configuration
The signals of the 8085 microprocessor can be grouped into the following categories:
Essential for the operation of the microprocessor
Used to specify memory locations
Used for data transfer
Control the operation of the microprocessor
Handle external events
For serial communication
+5-volt power supply
Ground reference
Crystal or R/C network or LC network connections to set the frequency of internal clock generator. The frequency is internally divided by two. Since the basic operating timing frequency is 3 MHz, a 6 MHz crystal is connected externally.
Clock Output is used as the system clock for peripheral and devices interfaced with the microprocessor.
These are data bus and address multiplexed. Therefore, in addition to carrying data, it can also carry a lower order 8-bit address. Usually, the Latch is used to demultiplex these lines.
The lines deliver the lower order address bus A0-A7 in the first clock cycle of the opcode fetch operation. It serves as data bus D0-D7 in the IO/M read or write that follows. Data can be read or written by the CPU over these lines.
Address buses A8 through A15 are used to address memory locations.
The following five functional headings apply to the 8085 instruction set:
Instructions for moving (copying) data between registers or between memory locations and registers. Not a single data transfer transaction modifies the contents of the source register. As a result, data transport is a copying process.
Contains instructions for performing operations such as addition, subtraction, increment, and decrement. Following the execution of an instruction in this group, the flag conditions are changed.
This category includes instructions that carry out logical operations such as AND, OR, EXCLUSIVE-OR, complement, compare, and rotate. Following the execution of an instruction in this group, the flag conditions are changed.
This category includes instructions used to move the program's control from one memory region to another.
Contains instructions for stopping program execution and for handling interruptions.
These instructions transfer information from memory to registers or between registers and memory.
These instructions replicate information from one location to another.
The contents of the source are not altered throughout the copying process.
These instructions perform arithmetic operations such as addition, subtraction, increment, and decrement.
These instructions perform various logical operations with the contents of the accumulator.
This group of instructions alters the sequence of program execution either conditionally or unconditionally.
These instructions control machine functions such as Halt, Interrupt, or do nothing.
SIM (Set Interrupt Mask): This instruction is used to set the interrupt mask and to output data through SOD line.
RIM (Read Interrupt Mask): This instruction is used to read the interrupt mask and to input data through SID line.
A program's instructions must all function with data. The process of defining the data that an instruction is to operate on is known as addressing. The 8085 is equipped with five distinct addressing types:
The data is given in the instruction itself.
The instruction contains the address of the data.
The instruction identifies the register that contains the data.
The address of the data is available in a register.
The data to be operated is specified in the instruction itself.
The data is given in the instruction itself when using immediate addressing mode. The information will be included in the program's instructions.
The instruction contains the address of the data in direct addressing mode. It will be stored in memory. Data and program instructions can be kept in separate memory locations when using this addressing technique.
When using register addressing mode, the instruction identifies the register that contains the data.
In this style of instruction, the address of the data is available in a register named after the instruction. In this case, the address will be in the register pair while the data will be in memory.
When using implied addressing mode, the data to be operated is specified right in the instruction itself.